1. Field of the Invention
The present invention relates generally to heat exchangers and, more specifically, to a gettering system for brazing heat exchangers used in automotive vehicles in a controlled atmosphere brazing (CAB) furnace.
2. Description of the Related Art
It is known to provide automotive vehicles with heat exchangers such as condensers, evaporators, heater cores and coolers. These heat exchangers are alternating rows of tubes or plates with convoluted fins made of a metal material such as aluminum or an aluminum alloy. Previously, the heat exchangers have been brazed in a vacuum furnace. Recently, a process known as xe2x80x9ccontrolled atmosphere brazing (CAB)xe2x80x9d has been used with non-corrosive fluxes. The CAB process has been preferred over vacuum furnace brazing due to improved production yields, lower furnace maintenance requirements and greater braze process robustness.
It is also known for CAB furnace brazing that an inert gas such as nitrogen gas is used to provide a non-oxidizing atmosphere. Although considered to be non-oxidizing, nitrogen gas contains residual impurities, most notably oxygen and water vapor. Although the aluminum heat exchanger is pre-cleaned using alkaline cleaning agents that reduce the native aluminum oxide layer, the surface of the aluminum heat exchanger will re-oxidize in the CAB furnace due to the presence of the oxygen and water vapor in the nitrogen gas. To minimize re-oxidation of the aluminum heat exchanger during the brazing process, the oxygen and water vapor in the nitrogen gas may be purified to less than twenty parts per million (20 ppm).
Although CAB furnace brazing has worked well, it is desirable to provide a gettering system for brazing heat exchangers in a CAB furnace. Also, it is desirable to reduce the oxygen content in incoming nitrogen used during CAB furnace brazing. Further, it is desirable to provide CAB furnace brazing with cost effective for use in high volume processing of aluminum heat exchangers.
Accordingly, the present invention is a gettering system for a CAB furnace includes a nitrogen gas source to supply a nitrogen gas to a controlled atmosphere brazing (CAB) furnace and an active metal getter source disposed within the CAB furnace and being a sheet to remove oxygen and water vapor in the nitrogen gas, whereby heat exchangers are brazed during a controlled atmosphere brazing (CAB) process in the CAB furnace.
One advantage of the present invention is that a gettering system is provided for brazing heat exchangers in a CAB furnace. Another advantage of the present invention is that the gettering system uses an active metal getter source to remove residual gas impurities, namely oxygen and water vapor from inert gases to levels below 20 ppm for fluxless CAB furnace brazing of the aluminum heat exchanger assembly. Yet another advantage of the present invention is that the gettering system that reduces oxygen level in incoming nitrogen by as much as twenty-nine percent, leading to an ultra-purified braze atmosphere that allows for brazing of fluxless alloy compositions. Still a further advantage of the present invention is that the use of the active metal getter source allows fluxless CAB furnace brazing of evaporators, condensers, heater cores and radiators. A further advantage of the present invention is that the gettering system is compatible with current CAB furnace designs and could be incorporated directly into existing furnace muffles with similar effects.
Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.